1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a recording material such as an electrophotographic copying apparatus, a printer or a facsimile apparatus, and more particularly to an image forming apparatus in which the interior thereof is cooled.
2. Related Background Art
An image forming apparatus constituting a background technology of the present invention and utilizing an electrophotographic process or another recording method is shown in FIGS. 3, 4 and 5.
FIGS. 3, 4 and 5 are cross-sectional views of a laser beam printer 100.
In a laser beam printer 100, a conveying path for a recording material (hereinafter represented as sheet) P from recording material supply means S through transfer means (transfer roller 9) to fixing means F generally has three configurations: namely a substantially horizontal configuration as shown in FIG. 3, an inclined configuration as shown in FIG. 4, and a substantially vertical configuration as shown in FIG. 5.
In the laser beam printer 100 shown in FIG. 3, a lower end of a sheet feeding tray 6 and a sheet feeding roller 2 are positioned at a right side of the apparatus, while a transfer roller 9 is positioned at the center of the apparatus, and a fixing device F is positioned at a left side of the apparatus, thereby realizing a substantially horizontal conveying path. Also above the sheet conveying path, there are provided image forming means such as a process cartridge C, and light source means such as a laser scanner 5.
Such sheet feeding roller, the conveying path, the light source means, the image forming means and the fixing device execute in succession a feeding of the sheet P, a transfer of a visible image (toner image) onto the sheet P, and a fixation by heating of the visible image on the sheet P.
A size reduction of the printer decreases the heat capacity thereof because of a decrease in the volume of the printer itself, thereby showing a significant increase in the internal temperature of the apparatus. Therefore, in a compact printer, the fixing means may be positioned in an upper part of the printer, in order to increase a heat discharging efficiency. More specifically, as shown in FIG. 4, a sheet feeding tray 6 and a sheet feeding roller 2 constituting the recording material supply means are positioned in a lower side of the apparatus, while a transfer roller 9 constituting the transfer means is provided at the central portion of the apparatus, a fixing device F as the fixing means is positioned obliquely above the transfer roller 9, and an external cover, covering the fixing device F, is provided with a louvered aperture 63 for efficiently discharging the heat of the fixing device F to the exterior of the apparatus.
In such case, the conveying path is provided in an inclined position. In such inclined configuration of the conveying path, image forming means such as a process cartridge C and optical source means such as a laser scanner 5 are positioned at a same height as or lower than the fixing device F to execute a feeding of a sheet P, a transfer of the visible image onto the sheet P and a fixation of the visible image on the sheet P in succession. The sheet P after image fixation in the fixing device F assumes a position with a printed surface downward by passing through a curved discharge guide, and is discharged onto a sheet discharge tray 14 by paired discharge rollers 12.
Also a pursuit for a further size reduction of the printer and for a faster speed thereof, particularly a shorter time for the output of a first page (first printout time), leads to a printer configuration as shown in FIG. 5, in which the sheet conveying path becomes substantially vertical and minimized.
Referring to FIG. 5, in recording material feeding means S, plural sheets P are stacked on a sheet feeding tray 6. The sheet P is separated one by one by a sheet feeding roller 2 provided at the left side (rear side) of the sheet feeding tray 6, and is conveyed by conveying rollers 3a, 3b along a first guide member 52 to a transfer roller 9 constituting the transfer means.
Referring to FIG. 5, a registration sensor 4 synchronizes a leading end position of the sheet P with a light emission timing of a laser scanner 5 serving as an exposure light source, thereby writing an image from a predetermined position on the sheet P.
A process cartridge C integrally includes process means such as a photosensitive member 8 serving as an image bearing member, a toner container 60, a developing device 17, a charging roller 18 serving as a charging device, a cleaning blade 19, a cleaning container 61 etc. and is detachably mounted on the printer.
A transfer roller 9 transfers a visualized image on the photosensitive member 8 onto the sheet P. Toner which is not transferred by the transfer means including the photosensitive member 8 and the transfer roller 9 but remains on the photosensitive member 8, namely so-called residual toner, is removed off from the photosensitive member 8 by the cleaning blade 19 and is recovered into the cleaning container 61. The cleaning blade 19 is formed by an elastic member such as silicone rubber.
The sheet P after passing the transfer roller 9 is guided substantially vertically, as explained before, by a second guide member 10, and enters the fixing device F which fixes the aforementioned visible image onto the sheet P. The fixing device F is constituted of a rotatably supported pressure roller 11 and a heater unit H including a heat generating member. In the fixing device F, the heater unit H is maintained in contact with the pressure roller 11 under a predetermined pressure, and, when the sheet P passes between the pressure roller 11 and the heater unit H, the image is fixed to the sheet surface by heat and pressure.
After the image fixation in the fixing device F, the sheet P is discharged by paired discharge rollers 12 onto a sheet discharge tray 14.
The process cartridge C includes various components susceptible to heat (hereinafter represented as heat-susceptible parts) such as the toner, the photosensitive member 8, the developing device 17 including a developer carrying member, the charging roller 18, the cleaning blade 19 etc. In particular, the toner around the developing device loses the charging property at 45–50° C. or higher, thereby resulting in an image defect. Particularly within the process cartridge C, the cleaning blade 19, being constituted of an elastic material such as silicone rubber, may be curled up when softened by the heat from the fixing device F. Also the used toner particles collected by the cleaning blade 19 are fused and coagulate at a temperature of 60 to 70° C., so that appropriate recovery of the used toner may become impossible. An inappropriate recovery of the used toner may lead to an image defect such as a black streak.
In case, as shown in FIG. 5, the conveying path for the sheet P from the recording material supply means through the transfer means to the fixing means is provided substantially vertically and components of the printer are so positioned as to achieve a further compact configuration, the fixing device F is often positioned close to the process cartridge C, and, even when the fixing device F is positioned higher than the process cartridge C, the heat of the fixing device F may be transmitted to the process cartridge C thereby inflicting an detrimental influence on the process cartridge C.
In order to avoid such drawbacks, it is conceivable to sufficiently separate the process cartridge C from the fixing device F thereby reducing transmission of heat therefrom to the process cartridge C and thus suppressing the temperature elevation in the components of the process cartridge C.
However, an increased distance between the process cartridge C and the fixing device F results not only in an increase in the dimension of the entire apparatus but also in an increase in the first printout time.
There is also proposed an image forming apparatus equipped with a fan 70 for forcedly exhausting the hot air from the apparatus or inhaling the external air into the apparatus thereby preventing a temperature elevation in the apparatus.
FIGS. 6, 7 and 8 illustrate such an image forming apparatus, respectively showing configurations in which the fan 70 is provided at a lateral side, an upper side or a back side of the apparatus.
In the image forming apparatus shown in FIG. 6, a fan 70 located at a lateral side of the apparatus exhausts the air from the apparatus or inhales the external air along a transversal direction of the sheet P, as indicated by an arrow in the illustration, thereby suppressing the temperature increase in the apparatus.
Also in the image forming apparatus shown in FIG. 7, a fan 70 located at an upper side of the apparatus exhausts the air from the apparatus to the exterior, as indicated by an arrow in the illustration, thereby suppressing the temperature increase in the apparatus.
Also in the image forming apparatus shown in FIG. 8, a fan 70 located at a back side of the apparatus exhausts the air from the apparatus or inhales the external air, as indicated by an arrow in the illustration, thereby suppressing the temperature increase in the apparatus.
However, in such image forming apparatus equipped with the fan 70, in case of the configuration shown in FIG. 6, as the air is exhausted or inhaled through the lateral side of the apparatus, the sheet becomes uneven in a temperature-humidity distribution in the transversal direction and may show an uneven curl in the transversal direction after passing the fixing device F.
Also in the image forming apparatus shown in FIG. 7, in which the fan 70 is positioned at an upper side and outside the width of the sheet for exhausting the hot air from the apparatus, the sheet likewise becomes uneven in the temperature-humidity distribution in the transversal direction, whereby a detrimental effect may be inflicted on the sheet curling after the fixation.
Further, in case the fan 70 is positioned at the back side as shown in FIG. 8, the process cartridge C which is most susceptible to heat and the fan 70 are mutually opposed across the conveying path for the sheet P. Therefore, the air circulated by the fan 70 is intercepted by such conveying path and cannot reach the process cartridge C, thus resulting in a poor cooling efficiency for the process cartridge C.
Besides, any of the configurations shown in FIGS. 6 to 8 is not favorable in the external appearance of the apparatus, with the fan 70 extruding from the outer wall of the apparatus or with the louver for covering the fan 70 being exposed to the exterior.
Also a configuration in which the fan 70 does not protrude from the outer wall leads to a larger apparatus as a space for installing the fan 70 has to be secured inside the apparatus.
Also in case the fan is exposed to the outer wall of the apparatus, disturbing noises are generated by the motor and the fan 70.
Furthermore, in any of the configurations shown in FIGS. 6 to 8, as the process cartridge C, which is most vulnerable to heat, is in a position distant from the fan 70, a large fan is required for sufficiently cool the process cartridge C, thus constituting an obstacle in realizing a smaller dimension, a lower cost and a lower noise level.